The present invention relates to sealing devices, and more particularly to a system for sealing a pressurized cylinder having an elongated longitudinal slot through which a shuttle of an aircraft catapult travels at high speed.
In the field of aircraft catapults, cylindrical members having elongated longitudinal slots therein have been used to permit connection between a pressure-driven piston member that travels within the cylinder and a shuttle that carries or tows the aircraft to be launched. Such a slotted cylinder requires a means for sealing the slot in order to maintain operating pressure within the cylinder, and a variety of sealing devices have been devised for this purpose. One such type of seal devised for use in the slotted cylinder comprises essentially a single, elongated, ribbon-like strip held in place along the slot by tension applied to the ends of the strip. During operation of the catapult, the sealing strip is guided internally of the cylinder as the piston and shuttle travel therethrough by a cam-like surface on the moving piston.
While such a flexible, dynamic seal as described above has proven satisfactory in the slotted cylinders of aircraft catapults for lower shuttle speed and shorter operating strokes, problems have arisen in their use in catapults generating high shuttle speeds over extended operating strokes because of an increased tendency of the ribbon-like strips to whip forward of the moving piston under such conditions. Whipping of the strip forward of the piston produces a random wave motion in the strip that adversely effects the operation of the pressurized cylinder regardless of whether the cylinder is being used to launch the aircraft by accelerating the shuttle or to brake the shuttle after launch. Random wave motion of the strip can cause the strip to buckle and break thereby resulting in a loss of driving pressure behind the piston in the rearward chamber of the launch cylinder. In the case of a braking application where the forward chamber pressure of the cylinder should be maintained, unseating of the sealing strip caused by the random wave motion thereof renders the seal ineffective to maintain forward braking pressure in the cylinder.
Existing sealing strip systems for the slotted cylinders of aircraft catapults have not adequately resolved the problem of effectively supporting the sealing strip along the entire length of the slot to prevent whipping of the strip. Closures of this type have been devised that utilize fluid pressure within the cylinder to force the strip upwardly against the edge of the slot. However, such closures rely on the integrity of the closure itself to maintain the pressure which provides the seal of the closure, and accordingly a rupture at any point along the length of the closure will cause the very force, which holds the closure in sealed position, to be lost. Furthermore, such an application of the fluid pressure to the forward chamber of the cylinder in order to support the sealing strip acts in opposition to the driving pressure in the rearward chamber of the launch cylinder thereby resulting in the inefficient utilization of launch power.